This invention relates generally to electronic watt-hour meters and more particularly to a shield for a current transformer in an electronic watt-hour meter.
Referring to FIG. 1, a top view, and FIG. 2, a perspective view, of a known electronic watt-hour meter 102 are shown. Electronic watt-hour meter 102 is used to measure usage of electricity. Electronic watt-hour meter 102 may include a meter base 103 and at least one current transformer 104 with a potential link 106 running through each current transformer 104. Other components included in electronic watt-hour meter 102 may include, for example, a surge suppressor 105, a current transformer cable 107, and metrology circuitry bracket 109. A current is measured by a metrology circuitry (not shown) in electronic watt-hour meter 102 and used in the calculation of energy usage.
Referring to FIG. 3, a perspective view, of a known current transformer 104 and known potential link 106 are shown. A potential link current flow 122 (shown by arrow) through potential link 106 may produce a current transformer magnetic field 116 in current transformer 104. Current transformer magnetic field 116 may moves circularly through a ferrite core (not shown) of current transformer. Current transformer magnetic field 116 may cause a current transformer current flow 117 in current transformer 104 directly proportional to the number of windings 119 in current transformer 104 and potential link current flow 122.
Referring to FIG. 4, a simplified top view of electronic watt-hour meter 102 is shown for illustrative purpose. If an external magnet 108 is placed in proximity to current transformer 104, then current transformer 104 is affected by an external magnet magnetic field 115 from external magnet 108. External magnet 108 may saturate a current transformer 104, thereby reducing its ability to accurately induce a proportional current in the windings (not shown) of current transformer 104. This reduction in performance results in a lower value of current flowing in the current transformer 104 and an incorrect electricity usage calculation. Use of an external magnet 108 for this purpose may result in theft of electricity. Shielding of the current transformer 104 may result in reducing the effect of the external magnet 108 on the current transformer 104.